net.sf.saxon.s9api

## Class XPathSelector

- java.lang.Object
- - net.sf.saxon.s9api.XPathSelector

- All Implemented Interfaces:
    Iterable<XdmItem>

      public class XPathSelector
      extends Object
      implements Iterable<XdmItem>

  An XPathSelector represents a compiled and loaded XPath expression ready for execution. The XPathSelector holds details of the dynamic evaluation context for the XPath expression.

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `XPathSelector(XPathExpression exp, ArrayList<XPathVariable> declaredVariables)`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `effectiveBooleanValue()` Evaluate the XPath expression, returning the effective boolean value of the result.
    `XdmValue` | `evaluate()` Evaluate the expression, returning the result as an `XdmValue` (that is, a sequence of nodes and/or atomic values).
    `XdmItem` | `evaluateSingle()` Evaluate the XPath expression, returning the result as an `XdmItem` (that is, a single node or atomic value).
    `XdmItem` | `getContextItem()` Get the context item used for evaluating the XPath expression.
    `XPathDynamicContext` | `getUnderlyingXPathContext()` Get the underlying dynamic context object.
    `URIResolver` | `getURIResolver()` Get the URI resolver.
    `Iterator<XdmItem>` | `iterator()` Evaluate the expression, returning the result as an `Iterator` (that is, an iterator over a sequence of nodes and/or atomic values).
    `void` | `setContextItem(XdmItem item)` Set the context item for evaluating the XPath expression.
    `void` | `setURIResolver(URIResolver resolver)` Set an object that will be used to resolve URIs used in fn:doc() and related functions.
    `void` | `setVariable(QName name, XdmValue value)` Set the value of a variable

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### XPathSelector

          protected XPathSelector(XPathExpression exp,
                       ArrayList<XPathVariable> declaredVariables)

  - ### Method Detail

    - #### setContextItem

          public void setContextItem(XdmItem item)
                              throws SaxonApiException

      Set the context item for evaluating the XPath expression. This may be either a node or an atomic value. Most commonly it will be a document node, which might be constructed using the `DocumentBuilder.build(javax.xml.transform.Source)` method.
      Parameters:
        `item` - The context item for evaluating the expression. Must not be null.
      Throws:
        `SaxonApiException` - if an error occurs, for example because the type of item supplied does not match the required item type

    - #### getContextItem

          public XdmItem getContextItem()

      Get the context item used for evaluating the XPath expression. This may be either a node or an atomic value. Most commonly it will be a document node, which might be constructed using the Build method of the DocumentBuilder object.
      Returns:
        The context item for evaluating the expression, or null if no context item has been set.

    - #### setVariable

          public void setVariable(QName name,
                         XdmValue value)
                           throws SaxonApiException

      Set the value of a variable
      Parameters:
        `name` - The name of the variable. This must match the name of a variable that was declared to the XPathCompiler. No error occurs if the expression does not actually reference a variable with this name.
        `value` - The value to be given to the variable.
      Throws:
        `SaxonApiException` - if the variable has not been declared or if the type of the value supplied does not conform to the required type that was specified when the variable was declared

    - #### setURIResolver

          public void setURIResolver(URIResolver resolver)

      Set an object that will be used to resolve URIs used in fn:doc() and related functions.
      Parameters:
        `resolver` - An object that implements the URIResolver interface, or null.
      Since:
        9.4

    - #### getURIResolver

          public URIResolver getURIResolver()

      Get the URI resolver.
      Returns:
        the user-supplied URI resolver if there is one, or the system-defined one otherwise
      Since:
        9.4

    - #### evaluate

          public XdmValue evaluate()
                            throws SaxonApiException

      Evaluate the expression, returning the result as an `XdmValue` (that is, a sequence of nodes and/or atomic values).

      Note: Although a singleton result may be represented as an `XdmItem`, there is no guarantee that this will always be the case. If you know that the expression will return at most one node or atomic value, it is best to use the `evaluateSingle` method, which does guarantee that an `XdmItem` (or null) will be returned.

      Returns:
        An `XdmValue` representing the results of the expression.
      Throws:
        `SaxonApiException` - if a dynamic error occurs during the expression evaluation.

    - #### evaluateSingle

          public XdmItem evaluateSingle()
                                 throws SaxonApiException

      Evaluate the XPath expression, returning the result as an `XdmItem` (that is, a single node or atomic value).
      Returns:
        an `XdmItem` representing the result of the expression, or null if the expression returns an empty sequence. If the expression returns a sequence of more than one item, any items after the first are ignored.
      Throws:
        `SaxonApiException` - if a dynamic error occurs during the expression evaluation.

    - #### iterator

          public Iterator<XdmItem> iterator()
                                     throws SaxonApiUncheckedException

      Evaluate the expression, returning the result as an `Iterator` (that is, an iterator over a sequence of nodes and/or atomic values).

      Because an `XPathSelector` is an `Iterable`, it is possible to iterate over the result using a Java 5 "for each" expression, for example:

           XPathCompiler compiler = processor.newXPathCompiler();
           XPathSelector seq = compiler.compile("1 to 20").load();
           for (XdmItem item : seq) {
             System.err.println(item);
           }

      Specified by:
        `iterator` in interface `Iterable<XdmItem>`
      Returns:
        An iterator over the sequence that represents the results of the expression. Each object in this sequence will be an instance of `XdmItem`. Note that the expression may be evaluated lazily, which means that a successful response from this method does not imply that the expression has executed successfully: failures may be reported later while retrieving items from the iterator.
      Throws:
        `SaxonApiUncheckedException` - if a dynamic error occurs during XPath evaluation that can be detected at this point. It is also possible that an SaxonApiUncheckedException will be thrown by the `hasNext()` method of the returned iterator.

    - #### effectiveBooleanValue

          public boolean effectiveBooleanValue()
                                        throws SaxonApiException

      Evaluate the XPath expression, returning the effective boolean value of the result.
      Returns:
        a `boolean` representing the effective boolean value of the result of evaluating the expression, as defined by the rules for the fn:boolean() function.
      Throws:
        `SaxonApiException` - if a dynamic error occurs during the expression evaluation, or if the result of the expression is a value whose effective boolean value is not defined (for example, a date or a sequence of three integers)
      Since:
        9.1

    - #### getUnderlyingXPathContext

          public XPathDynamicContext getUnderlyingXPathContext()

      Get the underlying dynamic context object. This provides an escape hatch to the underlying implementation classes, which contain methods that may change from one release to another.
      Returns:
        the underlying object representing the dynamic context for query execution

Copyright (c) 2004-2013 Saxonica Limited. All rights reserved.